I think it depends on what you mean by "readable." The first example clearly points to program logic and should be understood by anyone with a programming background.
For me, the second example is more intuitive based on the context (i.e. you take an array (or some other type of collection) and execute a method called Sum for each element of this array). The only place where the second example may become less clear is the actual lambda expression, especially for those who have no previous experience with lambdas or alraedy, there is a background in functional programming.
I think that as lambdas become more common in .NET programming, this will become less of a problem. Be that as it may, I think there is a very small learning curve to understand the basics of using lambda expressions in .NET.
Scott dorman
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